Potassium Carbonate

From weak carbonic acid (it isunstable and can exist only in dilute solutions), when interacting with alkalis, acidic and middle salts are obtained, which are otherwise called hydrocarbonates and carbonates, respectively. The reaction equations can be written: H2CO3 + KOH → KHCO3 + H2O and H2CO3 + 2KOH → K2CO3 + 2H2O. In the first, potassium hydrogen carbonate is obtained, and in the second, potassium carbonate. The formula of the acid salt is KHCO3, and the average is K2CO3. The molar mass of potassium carbonate is 138.2 g / mol. In appearance, the salt resembles a white, fine crystalline powder that is not combustible, melts at 891 C, without reaching the boiling point, the salt decomposes. Potassium carbonate is hygroscopic, readily soluble in water: in 100 ml at 20 ° C - 110.5 g, and at 100 ° C - 156 g salt. But in alcohol or in acetone this substance does not dissolve.

In the old days potassium carbonate was called potash, the wordcame from the Latin name "potassa". Carbonic acid is one of the oldest salts that have been known to people for a long time. In Europe, until the last century, potash was one of the most important chemical reagents of industrial importance. In Russia, a monopoly was established in 1721 for the production of potash by Peter the Great. Currently, on the territory of the Russian Federation, as well as in Armenia, Kazakhstan, Belarus, Ukraine, Turkmenistan, Moldova, Uzbekistan, this chemical is covered by the interstate standard GOST 10690-73. Potash belongs, according to GOST 12.1.005-88, to substances of the third hazard class, when exposed to mucous membranes or moist skin causes irritation.

If you mix potassium carbonate with water, then with itsdissolving a lot of heat, that is, the reaction of hydrolysis of K2CO3 is exothermic, and the formation of new substances under the action of water. The salt of dibasic carbonic acid is hydrolyzed stepwise. First, an acid salt is formed: H2O + K2CO3 → KHCO3 + KOH. Then the second stage of decomposition with water of already acidic salt proceeds weakly: H2O + KHCO3 → H2CO3 + KOH. Since the hydrolysis of potassium carbonate, like other salts of weak acids, proceeds with the formation of OH- hydroxyl ions, the pH of their aqueous solutions is always more than 7, and the medium is alkaline.

Carbonic potassium in the 17th century in Russia receivedleaching of wood ash. In wooden troughs, a solution of alkali was prepared, pouring ashes with hot water. Then this solution was poured into a brick hearth with burning wood. The potassium carbonate was crystallized by a very dense layer on the bottom of the hearth, with the help of scrap the potash was mined and laid out in barrels, clogging them sealed. It required a certain skill to allow the solution to evaporate, and the fire did not dry out. Therefore, the craft of "polivachs" was beginning to be taught in adolescence, and only after a few years the worker acquired certain skills and became a master of his craft. For example: when burning a fire, white ash is always formed, most of it is potash. Today, another industrial method has been realized: carbon dioxide is passed through the electrolysis of potassium carbonate: 2KOH + CO2 → K2CO3 + H2O. The result is potash and water.

Potassium carbonate is used in the production of soap andglass. In the laboratory, it is used as a soft desiccant in cases where other agents, such as calcium chloride or magnesium sulfate, are not allowed. It is not suitable for drying acidic compounds, but can be used to dry organic products with a low content of acidic impurities. Potassium carbonate is used to extinguish fires of class B, since it refers to chemical powders that can both inhibit and extinguish the combustion process. It has more fire-extinguishing efficacy than salts such as sodium carbonate, sodium sulfate, sodium fluoride or sodium hydrogen carbonate. Its inhibitory efficiency of combustion processes is also higher than that of sodium carbonate, sodium sulfate, aluminum oxide and calcium carbonate. In the glass industry, K2CO3 is used in the manufacture of laboratory (refractory), optical or potash glass, as well as glass for making dishes. In addition, potassium carbonate is in demand in the chemical, agricultural, medical, food industries.